What O. said.
(crosspost - and C's last paragraph. Fast/Multi-casting is great for combat magi - not sure if this is him. As C said - "Do a few things really well", and "combat" won't be one without several more Virtues in that direction. If he does take Spell Mastery, he'll certainly use it - just not sure it's where this one wants to go.)
For a new player, I'll avoid the complexities and subtleties of some suggestions. There are "concept characters" that are a lot of fun to play, but are not as simply, generically "strong" as otherwise. And I think you're looking to have your fun with "simply strong" first, at least by some common yardstick.
Many Virtues give 50 xp in some field, possibly with an additional access to an otherwise restricted Ability set - Arcane Studies, Education, Warrior, etc. (Magi have "all access", so that's not an extra attraction with those.) Skilled Parens gives 60 pts, plus the +30 pts in spells - hard to beat it if that's the direction you want. Saves the equiv of 6 years of pre-apprentice years, 3 of post-, and about 3 years of in-game study - a nice headstart. (Educated or Arcane Studies on top of that isn't as strong but isn't bad either, and makes sense story-wise for a Bonisagus.)
Puissant with Art is better than Affinity unless you want to go over a total of 13 (10+3 Puissant) in that Art (for your mage's age)- that requires an Affinity (see page 32, col iii, top). If you're going big (but not "too" big), go Puissant. (And similarly with Puissant Abilities, if with diff limits - see chart page 31, col i.)
(Sounds like your mage will take Puissant with Intrigue as their free House virtue, from page 30, unless they were forced to take Psst Mag Theory by their Parens (your choice, purely "back story"). Taking both, one as a free and one as a "bought" virtue, is not a bad choice either - Magic Theory is key to lab work, and your mage will be in the lab, trust me.)
Inventive Genius is another great foot-up in the lab, and another widely popular virtue. You won't regret it.
For a simple Major Magical Virtue for a starting player, I'd recommend Mythic Blood. Others can certainly work, but this is simple and clean, and user-friendly. Keeps your mage from getting fatigued during spell casting ( a common pitfall for new players), has a free "magical effect" (which can be outside your Arts, saving study in that direction), and gives a free Minor Magical Focus (but max is 1 MF/mage) - which makes him strong in one narrow type of spell effect. (And means that higher-magnitude spells in that area are now within reach.)
Strong Faerie Blood isn't bad - gives a +1 to Presence (a social stat, and he's going to be a social animal), gives free Second Sight (always handy), negates penalties for casting in a Fae Aura, and gives him a better starting point when negotiating with Fae. (Those last can be more or less important depending on the saga and character's in-game choices, but you never know what will happen.) Whether all that is worth a +3 pts Major Virtue is up to you (and your final math).
Then, if he really wants to be the politico, I'd recommend something like Gossip and/or Social Contacts (the latter esp if he's pumped Presence.)
And, as suggested, don't get seduced by Flaws that come with negative Hermetic Social penalties. Mage up, take about 5 pts of Magical Flaws, take a Major Story Flaw and some Personality Flaws that you can RP, and call it good.
(And as I do about twice a year, I'll plug this again, with apologies for those who've already read it:
A "How to" of Magi CharGen for the Boggled